Code

==============================================
= Arduino SOS CAll sim900 shield Project =
= with Arduino =
= http://www.mrmodder.com =
==============================================
#include "SIM900.h"
#include <SoftwareSerial.h>
#include "call.h"

#define ACTIVE LOW

const int ledPin = 13; // the number of the LED pin

CallGSM call;
boolean started=false;
int buttonState = 1;
const int buttonPin = 7; // the number of the pushbutton pin
boolean calling = false;

void setup()
{

Serial.begin(9600);
pinMode(ledPin,OUTPUT);
pinMode(buttonPin, INPUT);
digitalWrite(buttonPin,HIGH);
if (gsm.begin(9600))
{
Serial.println("\nstatus=READY");
started=true;
}
else
Serial.println("\nstatus=IDLE");
}

void loop()
{
buttonState = digitalRead(buttonPin);
if (buttonState == ACTIVE) {
if(calling)
{
digitalWrite(ledPin,LOW);
calling = false;
call.HangUp();
delay(1000);
}else
{
calling = true;
digitalWrite(ledPin, HIGH);
delay(1000);
call.Call("+300000000000"); //Insert telephone number here

}